Hermetically sealed alkaline storage battery



Nov. 7, 1967 HERMANN-HANS VON Dol-:HREN 3,351,490

HERMETICALLY SEALED ALKLINE STORAGE BATTERY Original Filed July '7. 1960United States Patent Otiice 3,351,499 Patented Nov. 7, 1967 3,351,490HERME'I'ECALLY SEALED ALKAMNE STRAGE BATTERY Hermann-Hans von Doehren,Frankfurt am Main, Germany, assigner to Vama Alrtiengeseiisehaft,Frankfurt am Main, Germany Continuation ot' application Ser. No. 41,441,July 7, 196i). This application Mar. 20, 1964, Ser. No. 354,500 SCtairns. (Cl. 13am-6) The present application is a continuation of mycopending application Ser. No. 41,441, filed Jul-y 7, 1960i, nowabandoned, and entitled Storage Battery.

The present invention relates to a storage battery and more particularlyto a storage battery including a positive electrode of the compositiondescribed below.

More specifically, the invention is concerned with hermetioally sealedstorage batteries, preferably those wi-th alkaline electrolyte such as`are for instance described in U.S. Patent 2,798,110 U.S. Patent2,842,607, British Patent No. 774,479, British Patent No. 774,478,British Patent No. 741,345, British Patent No. 769,784, British PatentNo. 782,394 and with positive electrodes which may be of widely varyingstructure such as sntered electrodes, press electrodes, pocketelectrodes, etc.

In order to increase the conductivity and to reduce the inner resistanceof electric storage batteries, particularly of those containing analkaline electrolyte, it is customary to admix to the regular positiveactive mass conductive materials such as graphite or nickel lakes. It isalso possible to provide suitable electrically conductive sinteredbodies, as carrier for the active mass of the positive electrode.

However, upon discharge of such battery cells, it is found that when theterminal voltage of the battery drops below one volt, i.e. at apotential at which only a very small and insignificant dischargecapacity remains, further drop `of the voltage is undesirably retarded.This intermediate voltage level seems to be caused by the formation ofactive oxygen during charging or operation of the battery and thisphenomenon occurs in connection with all electrodes which cannot beelectrochemically attacked. This intermediate voltage level isparticularly marked in connection with graphite containing electrodes inwhich the graphite is oxidized to a considerable extent by the activeoxygen formed during operation of the battery.

The length of time for which this intermediate voltage level ismaintained depends primarily on the charging and discharging conditions,the length of time which elapsed since the last charging of the battery,the composition `of the electrolyte and the size of the surface area ofthe conductive material in the electrode.

Particularly, with respect to hermetioally sealed batteries whichinclude safeguards against deep discharge with reversal of polarity,this intermediate voltage level is highly disadvantageous, since itcomplicates the proper proportioning of the capacities of the positiveand negative electrodes due to the dependence of the same on the factorsdiscussed in the preceding paragraph.

Due to the fact that it appears impossible and impractical to determineaccurately the length for which this inter-mediate voltage level will bemaintained in `any given battery, the above-discussed phenomenon greatlycomplicates hermetically sealed battery arrangements in which excessiveoverpressure is to be avoided, since the point or moment at whichreversal of polarity will occur cannot be predetermined with suflicientaccuracy. As stated above, the reversal of polarity will depend to someextent on the length of time for which the intermediate voltage level ismaintained and thus a somewhat indeterminable and variable factor has tobe taken into account.

It is therefore an object of the present invention to overcome the4above-discussed ditiiculties broadly and particularly with respect tohermetically sealed alkaline storage batteries, in which the active massof the positive electrode contains current conducting flakes, sinterbodies or the like. v

It is another object of the present invention to eliminate formation ofthe above discussed intermediate voltage level so that upon exhaustionor" the active material of the positive electrode the terminal volta-gewill drop quickly without formation of an intermediate potential, to thepotential of the electrode of opposite polarity, Le. of the negativeelectrode and the potential of anti-polar mass if such anti-polar massis included in the positive electrode.

Other objects and advantages of the present invention will becomeapparent from a further reading of the description and appended claims.l

With the above and Aother objects in view the present inventioncontemplates in a storage battery, in combination, positive and negativeelectrodes, and an electrolyte in contact with the electrodes, thepositive electrode including regular active mass having distributedtherethrough an effective amount of at least one substance which isinsoluble in the electrolyte and capable of alternating between a higherand `a `lower valency so as to form within the positive electrode anauxiliary redox system such that the oxygen potential relative to theauxiliary redox system is at least equal to the oxygen potential againstthe regular active mass of the positive electrode.

Thus, according to the present invention, the establishment of theVintermediate potential oi-,voltagge level is prevented by distributingin the active mass of the positive electrode a substance which isinsoluble in the electrolyte, for instance, in the alkaline electrolyteof the hermetically sealed alkaline storage battery, which subp stancecan be easily changed from a lower to a higher valenceland vice versa,so that the positive electrode will possess an additional redoxpotential against which the free oxygen potential will be at least equalto or greater than the` oxygen potential against the regular active massof the positive electrode.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of speciiicembodiments when read in connection with the accompanying drawings, inwhich:

FIG. 1 is a schematic cross-sectional view of `a battery incorporatingthe present invention;

FIG. 2 is a schematic elevational cross-sectional view of anotherbattery in accordance with the present invention;

FIG. 3 is a plan view in cross section illustrated in FIG. 2; and

FIG. 4 illustrates the potential curve during discharge of a sealedalkaline storage battery with and without the addition of ceriumhydroxide or the like in accordance with the present invention.

Referring now to the drawings and particularly to FIG. 1, the upperportion 1 and the lower portion 2 of the housing are shown, preferablymade of metal. In the areas where housing portions 1 and 2 overlap eachother yan insulating intermediate layer 3 is provided, consisting ofrubber or of a synthetic material such as a polyamide. The electrodepair 6 and 7 is arranged within the housing and separated by interposedseparator 8. Advantageously,

of the battery electrodes 6 and 7 as well as separator 8 are formed withfine pores, Separator 8 may also consist of a densely woven or otherwiseproduced fabric, or of a lter paperlike material made of natural orsynthetic bers, or of a semi-permeable foil of regenerated cellulose, ofa microporous synthetic membrane or the like, or of a combination ofseveral layers of the above materials. Electrodes 6 and 7 possess largesurface areas which are in contact with the gas space within thebattery. These areas are indicated in FIG. 1 by reference numerals 9 and10 denoting opposite faces of electrodes 6 and 7, respectively, whichserve for the electrochemical reaction of the gases. To maintain theelectrode faces 9 and 10 spaced from the inner walls of housing portions1 and 2, spaces 4 and 5 are provided formed as a framework withrelatively large open intermediate spaces. It is necessary to maintainthe electrodes spaced from the housing in order to provide sufficientcontact area between the gases formed during the operation of thebattery and the electrodes. Spaces 4 and 5 preferably consist of metalso as to form conductive connections between the respective electrodesand housing portions. At least one of spaces 4 and 5 possesses a certinadegree of resiliency. No special connections to the terminals of thebattery are needed due to the metallic spaces 4 and 5. The gas spaceincludes in addition to the 4areas between electrode face 10 and housingportion 1, and electrode face 9 and housing portion 2, also the areasindicated by reference numerals 11 and 12, which, however, are of lessersize and effectiveness than the areas between the electrodes and thehousing.

The battery illustrated in FIGS. 2 and 3 is basically constructed in amanner somewhat similar to the battery illustrated in FIG. 1.

Housing 13 is closed by bottom plate 14 and cover member 15. Elements13, 14 and 15 are preferably made of metal. Terminals 16 and 17penetrate through cover member 15 and are insulated against the same.Terminals 16 and 17 are in contact with the positive and negativeelectrodes within the cell by means of electrical conduits 18 and 19.Terminal 16 is thus connected with electrodes 20 and 22, and terminal 17with electrodes 21, 23 and 24. Electrodes 20 and 22 form electrodepairs, respectively, and similarly electrodes 23 and 24 form pairs,while electrodes 21 outwardly delimit the set of electrode plates.Spaces 26 are located between electrodes 20 and 22, as well as betweenelectrodes 23 and 24. Spaces 25 are provided between the walls ofhousing 13 and outermost electrodes 21. Spaces 25 and 26 preferablyconsist of metal and serve for electrically connecting the splitpositive and negative electrodes, respectively, as well as the housing.Due to the placing of spaces 25 and 26 between electrodes 20 and 22, 23and 24, and between housing 13 and electrodes 21, a gas accessible areais formed within the battery. Thus, electrode faces 28, 29, 30, 31, 32,33, 34 and 35 serve for electrochemically disposing of the gases formedduring operation of the battery. These free electrode faces must becovered by a thin film of electrolyte. Between electrodes of oppositepolarity such as between electrodes 21 and 20, 22 and 23, 24 and 20, and20 and 22, separators 27 are arranged. In both illustrated batteries,the active mass of the positive electrode contains about 0.4% ceriumhydroxide.

It must be noted that the batteries which are illustrated and discussedabove are given by way of example only, the present invention not beinglimited to the specific structural arrangements of these batteries.

Referring now to FIG. 4 of the drawing, it will be seen that in a givenconventional hermetically sealed alkaline storage battery, the voltagewill drop upon discharge as indicated by full line I. After dischargingabout 5 ampere hours a rst voltage drop occurs from about 1.5 to about0.8 volt and a voltage of 0.8 volt or thereabouts is substantiallymaintained during further discharge to about 6.5 ampere hours. It isthis intermediate voltage level which is harmful and which is preventedaccording to the present invention.

The voltage curve according to the present invention is indicated bydotted line Il. It can be seen that the voltage drop upon discharge ofabout 51A: ampere hours is sudden and, without forming an intermediatelevel, continues to the potential of the negative electrode, i.e. to thepotential at which reversal of polarity might occur.

The intermediate potential of the active oxygen is thus avoidedaccording to the present invention by the addition of about 0.4% byweight of cerium hydroxide to the active mass of the positive electrode.

Surprisingly, it has been found that the above discussed results areobtained by admixing to the active mass effective quantities, preferablybetween 0.01% and 10% of oxides or hydroxides of lanthanum or relatedelements preferably cerium, or oxides or hydroxides of the group III-Bof the periodic table, i.e. gallium, indium or thallium.

As stated above, the quantity of the oxides or hydroxides forming theauxiliary redox system is preferably maintained between about 0.01% and10% by weight of the active mass of the positive electrode. However, ithas been found that in most cases the desired result can be safelyobtained with quantities of between 0.5% and 1% by weight, i.e. theaddition of between 0.5 and 1% by weight of oxides or hydroxides oflanthanum, cerium, gallium, indium or thallium has been found to beeffective in preventing formation of the undesirable intermediate oxygenpotential level. This is primarily so in connection withgraphite-containing electrodes in which other- Wise this intermediatepotential is strongly developed. However, the exact amount of theadditives such as cerium hydroxide or the like, depends also on thecurrent density with which the electrode plates are charged.

Generally, it has been found that such materials may be used inaccordance with the present invention as additives to the active mass ofthe positive electrode which can easily change at a high reaction speedfrom one valence to another. The effectiveness of these substances isprimarily dependent on quick change of the valence, such as for instancecan be accomplished in a system of CeIV/Cemhydroxide in an alkalineelectrolyte. Thereby, the formation of electrochemically active oxygenor peroxidic oxygen, will be prevented, whereby the cerium oxide orhydroxide or the like will act as an oxygen acceptor in the positiveelectrode. In order to act in this manner, the oxygen voltage orpotential at these acceptor substances must be at least equal to orlgreater than the corresponding oxygen potential with respect to theregular active mass of the positive electrode.

The foregoing can be yschematically represented as follows:

REDUCTION It is a further advantage that positive electrodes accordingto the present invention will speed up charging or formation of theelectrodes since during such charging 0r formation processes, theauxiliary redox system described above will also serve to transmitelectrochemically active oxygen. Particularly in the case ofgraphite-containing electrodes, the addition of substances forming theauxiliary redox system according to the present invention to thepositive electrode will for all practical purposes prevent oxydationofthe graphite to CO3 ions.

The following examples are given as illustrative only, the presentinvention however not being limited to the specic details of theexamples:

Example I For producing a positive pocket electrode plate, one part byweight of cerium-(IV)-sulfate, Ce(SO4).,H2O,

is dissolved in parts by weight of distilled water. 4 parts by Weight ofgraphite flakes are introduced in the thus formed solution andintimately mixed therewith. The thus formed paste is placed in a nickeldish and dried at about 105 C.

40 parts of 5% potassium hydroxide are now prepared and a quantity ofhydrogen peroxide is added thereto sur"- ticient to form a 1% alkalinehydrogen peroxide solution, The dried graphite cerium sulfate paste isnow stirred into the thus formed alkaline solution and, thereby, amixture of ceriumIV/-ceriumHI-hydroxide is precipitated. The precipitateis allowed to stand for about one hour in a precipitating solution andthereafter filtered and washed with distilled water until the spent washwater is free of sulfate and alkali. The filter cake is then thinlydistributed in nickel dishes and again -dried at 105 C. The thusobtained dry material which contains about 2% by weight ofceriumm/ceriuinw-hydroxide is then nely ground in a ball mill.

The thus pretreated graphite mass is then further processed inconventional manner into positive electrode plates as described inElektrochemie wssriger Lsungen by F. Foerster, 3rd edition (I. A.Barthe, Leipzig), vol. I, 1922, page 267.

Example Il A positive nickel sinter plate according to the presentinvention may be produced as follows:

The nickel sinter plate is immersed in an aqueous solution containingbetween 0.5% and 1% of Cerwin-(IV)- sulfate so that the interstices ofthe sinter structure will be impregnated with the solution. The plate isthen removed from the irnpregnating bath and dried at 105 C. Thereafter,the plate is immersed in a 5% aqueous potassium hydroxide solutioncontaining 1% hydrogen peroxide. Thereby a mixture ofceriumm/ceriurnIV-hydroxide is precipitated in the interstices of thesinter plate.

The thus prepared and still moist plates are then for some timecathodically polarized with a weak current in order to eliminate anionswhich may still be present in the plates. Thereafter, the plates areagain dried at 105 C. and subsequently active mass is applied inconventional manner, as described in S. W. Vinal, Storage Batteries, 4thedition, New York, 1955, page 100.

Examples for individual active positive masses with specic auxiliaryredox system:

Mass No. Redox system Composition of active mass applied La+++lLa++ 71w. percent Ni(OH)i-}20 w. percent Graphite+8-7 w. percent La(OH)a.Ce++++/Ce+++ 78.33 w. percent Ni(0H)2-|21.3 W. percont G1aphite+0.37 W.percent CeOz Ga+++/Ga++ 76.3 W. percent Ni(OH)ri-19.4 w. percentGraphite-H3 percent Ga(0H)e. .Tn+++/.l'n++ 78.2 w. percent Ni(OH)q{-20.4w. pei'- cent Graphite-HA percent In (OlzUs. Tl+++/Tl++ 80.7 w. percentNi(OH)q-tl8.9 w. percent Graphite-W25 W. percent. Tl (OHMI-0.15% w.percent T1(OH). Ce++++Ce+++ 78.6 W. percent Ni(OH)i+19.96 w. percentGraphite-|- Tl+++/Tl+ 0.16 W. percent Tl(OH);.

+0. 04 w. percent TMOII). -I-O. 24 W. percent CeOi It will be understoodthat each of the elements described above, or two or more together, mayalso find a useful application in other types of batteries diiferingfrom the type described above.

While the invention has been illustrated and described as embodied inthe positive electrode of a hermetically sealed alkaline storagebattery, it is not intended to be limited to the details shown, sincevarious modifications and structural changes may be made withoutdeparting in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specic aspects of this invention and,therefore, such adaptations should and are intended to be comprehendedwithin the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a hermetically sealed alkaline storage battery, in combination,positive and negative electrodes; and an alkaline electrolyte in contactwith said electrodes, said positive electrode including a majorproportion of nickel -oxide and a minor proportion of a currentconducting material selected from the group consisting of nickel andgraphite and having distributed therethrough between 0.01% and 2% byweight of said active mass of at least one substance selected from thegroup consisting of oxides and hydroxides of lanthanum, cerium.,gallium, indium and thallium and which is insoluble in said electrolyteand capable of alternating between a higher and a lower valency so as toform within said positive electrode an auxiliary redox system such thatthe oxygen potential relative to said auxiliary redox system is at leastequal to the oxygen potential of said nickel oxide of said positiveelectrode.

2. In a hermetically sealed alkaline storage battery, in combination,positive and negative electrodes; and an alkaline electrolyte in contactwith said electrodes, said positive electrode including a major portionof nickel oxide and a minor proportion of a current conducting materialselected from the group consisting of nickel and graphite and havingdistributed therethrough between 0.01% and 1% by weight of said activemass of at least one substance selected from the group consisting ofoxides and hydroxides of lanthanum, cerium, gallium, indium and thalliumand which is insoluble in said electrolyte and capable of alternatingbetween a higher and a lower valency so as to form within said positiveelectrode an auxiliary redox system such that the oxygen potentialrelative to said auxiliary redox system is at least equal to the oxygenpotential of said nickel oxide of said positive electrode.

3. In a hermetically sealed alkaline storage battery, in combination,:positive and negative electrodes; and an alkaline electrolyte inContact with said electrodes, said positive electrode including a majorproportion of nickel oxide and a minor proportion of a currentconducting material selected from the group consisting of nickel andgraphite and having distributed therethrough between 0.5% and 1% byweight of said active mass of at least one substance selected from thegroup consisting of oxides and hydroxides of lanthanum, cerium, gallium,indium and thallium and which is insoluble in said electrolyte andcapable of alternating between a higher and a lower valency so as toform within said positive electrode an auxiliary redox system such thatthe oxygen potential relative to said auxiliary redox sys-tem .is atleast equal to the oxygen potential of said nickel oxide of saidpositive electr-ode.

4. In a hermetically sealed storage battery including an alkalineelectrolyte, the improvement in combination therewith comprising apositive electrode in contact with said alkaline electrolyte andincluding a major proportion of nickel oxide and a minor proportion of acurrent conducting material selected from the group consisting of nickeland graphite and having distributed therethrough at least one substancebeing selected from the group consisting of oxides and hydroxides oflanthanum, cerium, gall-ium, indium and thallium, said substance -beinginsoluble in said electrolyte and present in .a quantity equal tobetween 0.01% and 1% of the weight of said nickel oxide.

5. In a hermetically sealed alkaline storage battery, in combination,positive and negative electrodes; and an 7 8 alkaline electrolyte incontact with said electrodes, said References Cited positive electrodeincluding a major proportion of nickel UNITED STATES PATENTS oxide and aminor proportion of a current conducting material selected from thegroupy consisting of nickel and dllson' 6 graphite and havingdistributed therethrough cerium hy- 5 2 9 l a ey 13 6 droxide in aquantity equal to about 0.4% by Weight of l.

said nickel oxide of said positive electrode, said ceriurn WINSlON A'DOUGLAS Pmnary Exammer' hydroxide being insoluble in said alkalineelectrolyte. B. OHLENDORF, A. SKAPARS, Assistant Examiners.

1. IN A HERMETICALLY SEALED ALKALINE STORAGE BATTERY, IN COMBINATION,POSITIVE AND NEGATIVE ELECTRODES; AND AN ALKALINE ELECTOLYTE IN CONTACTWITH SAID ELECTRODES, SAID POSITIVE ELECTRODE INCLUDING A MAJORPROPORTION OF NICKEL OXIDE AND A MINOR PROPORTION OF A CURRENTCONDUCTING MATERIAL SELECTED FROM THE GROUP CONSISTING OF NICKEL ANDGRAPHITE AND HAVING DISTRIBUTED THERETHROUGH BETWEEN 0.01% AND 2% BYWEIGHT OF SAID ACTIVE MASS OF AT LEAST ONE SUBSTANCE SELECTED FROM THEGROUP CONSISTING OF OXIDES AND HYDROXIDES OF LANTHANUM, CERIUM, GALLIUM,INDIUM AND THALLIUM AND WHICH IS INSOLUBLE IN SAID ELECTROLYTE ANDCAPABLE OF ALTERNATING BETWEEN A HIGHER AND A LOWER VALENCY SO AS TOFORM WITHIN SAID POSITIVE ELECTRODE AN AUXILIARY REDOX SYSTEM SUCH THATTHE OXYGEN POTENTIAL RELATIVE TO SAID AUXILIARY REDOX SYSTEM IS AT LEASTEQUAL TO THE OXYGEN POTENTIAL OF SAID NICKEL OXIDE OF SAID POSITIVEELECTRODE.